1. Field of the Invention
This invention relates to a laboratory material and, more particularly, to a stable blood serum conjugated bilirubin reference composition.
2. Description of the Prior Art
The relationships among bilirubin, its glucuronides, and the azo pigments are set forth in FIG. 22-3 of Henry et al., Clinical Chemistry, Principles and Technics, 2nd Edition, Harper & Row, New York, N.Y. (1974), p. 1040 (1). Bilirubin is also referred to in the art as either "unconjugated bilirubin" or "indirect bilirubin." In contrast, bilirubin monoglucuronide and bilirubin diglucuronide are referred to in the art as either "conjugated bilirubin" or "direct bilirubin." "Total bilirubin" is the sum of the unconjugated bilirubin and conjugated bilirubin present in the assayed sample.
The measurement of conjugated and unconjugated bilirubin levels in a patient's serum is necessary in order to diagnose various possible causes of hyperbilirubinemia. To assure the accuracy of such measurements, it is highly desirable to have stable reference compositions that can be employed either as a reference standard or as a reference control, i.e., to either calibrate an instrument or to periodically verify that the instrument is still operating within the tolerances desired, respectively.
Although there is literature suggesting ways to stabilize unconjugated bilirubin (2) and azobilirubin (3-5), literature with respect to the stabilization of conjugated bilirubin appears to be sparse (6). Furthermore, the only commercial reference composition containing a form of conjugated bilirubin is a lyophilized product which has a reconstituted shelf life of only 3 days when stored between 2.degree.-8.degree. C. (10).
Accordingly, it would be highly desirable to have a stable conjugated bilirubin reference composition. This stable conjugated bilirubin reference composition would be useful as both a control and a standard to assure the accuracy of clinical assays and thereby help to improve the accuracy of the diagnosis based upon such data.